Conventionally, as a prefilled syringe which is already filled with a medical substance, there is known a two-chamber syringe (so called dual syringe), as disclosed in Patent Document 1 for example, including a barrel which has two chambers each filled with a medical substance.
FIG. 12 shows a dual syringe 1 as disclosed in Patent Document 1. In the dual syringe 1, a push member 3 disposed in a generally cylindrical barrel 2 is moved toward a choked end 2a, to apply pressure to a plug 4 which partitions the inside space of the barrel 2. When the pressurized plug 4 moves toward the choked end 2a, the medical substance filled in a space 5 between the plug 4 and the choked end 2a is injected from an injection hole formed in the choked end 2a. Then, when the plug 4 reaches a recess (where the inner diameter is increased) 2b formed in an inner side surface of the barrel 2, the medical substance stored in a space 6 between the push member 3 and the plug 4 flows through a bypass formed between the plug 4 and the recess 2b, into the space 5.
Patent Document 1: JP-A 6-7446